1. Field of the Invention
The field of the invention pertains to implantable devices, and, more particularly, vaso-occlusive devices for the occlusion of body lumens and cavities.
2. Background of the Invention
In many clinical situations, blood vessels are occluded for a variety of purposes, such as to control bleeding, to prevent blood supply to tumors, and to block blood flow within an aneurysm.
Embolization of blood vessels is particularly useful in treating aneurysms. Aneurysms are abnormal blood filled dilations of a blood vessel wall, which may rupture causing significant bleeding. For the cases of intracranial aneurysms, the significant bleeding may lead to damage to surrounding brain tissue or death. Intracranial aneurysms may be difficult to treat when they are formed in remote cerebral blood vessels, which are very difficult to access. If left untreated, hemodynamic forces of normal pulsatile blood flow can rupture fragile tissue in the area of the aneurysm causing a stroke.
Vaso-occlusive devices have been used in the treatment of aneurysms. Vaso-occlusive devices are surgical implants placed within blood vessels or vascular cavities, typically by the use of a catheter, to form a thrombus and occlude the site. For instance, treatment of a stroke or other such vascular accident may include the placement of a vaso-occlusive device proximal of the site to block the flow of blood to the site and alleviate the leakage. An aneurysm may similarly be treated by introduction of a vaso-occlusive device through the neck of the aneurysm. The thrombogenic properties of the vaso-occlusive device cause a mass to form in the aneurysm and alleviate the potential for growth of the aneurysm and its subsequent rupture. Other diseases, such as tumors, may often be treated by occluding the blood flow to the tumor.
There are a variety of vaso-occlusive devices suitable for forming thrombi. One such device is found in U.S. Pat. No. 4,994,069, to Ritchart et al., the entirety of which is incorporated by reference. That patent describes a vaso-occlusive coil that assumes a linear helical configuration when stretched and a folded convoluted configuration when relaxed. The stretched configuration is used in placement of the coil at the desired site and the convoluted configuration occurs when the coil is ejected from the catheter and the coil relaxes. Ritchart et al. describes a variety of shapes, including “flower” shapes and double vortices. A random shape is described as well.
U.S. Pat. No. 6,280,457B1 to Wallace et al., describes an occlusive device comprising an inner core wire covered with a polymer. The polymeric material includes protein based polymers, absorbable polymers, non-protein based polymers, and combinations thereof. The polymer helps contribute to the formation of emboli for occlusion of a body cavity.
Vaso-occlusive coils having complex, three-dimensional structures in a relaxed configuration are described in U.S. Pat. No. 6,322,576B1 to Wallace et al. The coils may be deployed in the approximate shape of a sphere, an ovoid, a clover, a box-like structure or other distorted spherical shape. The patent also describes methods of winding the anatomically shaped vaso-occlusive device into appropriately shaped forms and annealing them to form various devices.
Vaso-occlusive coils having little or no inherent secondary shape have also been described. For instance, co-owned U.S. Pat. Nos. 5,690,666 and 5,826,587 by Berenstein et al., describe coils having little or no shape after introduction into the vascular space.
There are a variety of ways of discharging shaped coils and linear coils into a body cavity. In addition to those patents that apparently describe only the physical pushing of a coil out into the body cavity (e.g., Ritchart et al.), there are a number of other ways to release the coil at a specifically chosen time and site. U.S. Pat. No. 5,354,295 and its parent, 5,122,136, both to Guglielmi et al., describe an electrolytically detachable embolic device.
A variety of mechanically detachable devices are also known. Various examples of these devices are described in U.S. Pat. No. 5,234,437, to Sepetka, U.S. Pat. No. 5,250,071 to Palermo, U.S. Pat. No. 5,261,916, to Engelson, U.S. Pat. No. 5,304,195, to Twyford et al., U.S. Pat. No. 5,312,415, to Palermo, and U.S. Pat. No. 5,350,397, to Palermo et al.
Vaso-occlusive devices may be composed of biodegradable materials, such as polyglygolic acid polymer, and/or non-biodegradable materials, such as metal. Biodegradable vaso-occlusive devices may not have the required resilient or stiffness to form a desired three dimensional relaxed configuration. As such, it is desirable to have an improved vaso-occlusive device that does not require a convoluted or complex three dimensional relaxed configuration. Furthermore, it is also desirable to have an improved vaso-occlusive device that conforms better with the shape of a body cavity and has a more efficient space-filling capacity.